The present disclosure relates to a semiconductor apparatus, and more particularly, to a wide area radio frequency plasma source suitable for simultaneously ashing or etching multiple semiconductor substrates.
In ashing and etching applications, the use of radio frequency (RF) or microwave power is common. In induction RF plasma reactors, induction by RF occurs by generating a plasma discharge with a metal exciter i.e., electrode (typically in the form of a coil). Typically, in a capacitive discharge the wafer holder serves as an opposing electrode, while at the same time acts as a heating/cooling platen in order to maintain certain substrate temperature. The metal exciter is physically removed from the plasma discharge by a dielectric window of some sort, through which the high-frequency energy can be coupled. Having the metal exciter separated from the plasma discharge by a dielectric is necessary to prevent the plasma from striking the metal exciter and causing sputtering of metal from the exciter, which can deposit on the wafers leading to defects on the wafers, and substantially shorten exciter lifetime. As used herein, the term “wafer” shall mean any material substrate, including but not limited to silicon wafers, glass panels, dielectrics, metal films or other semiconductor material.
RF power at 13.56 MHz is predominantly used in plasma reactors because this frequency is an ISM (Industry, Scientific, Medical) standard frequency for which government mandated radiation limits are less stringent than at non-ISM frequencies, particularly those within the communication bands. The substantially universal use of 13.56 MHz is further encouraged by the large amount of equipment available at that frequency because of this ISM standard. Other ISM standard frequencies are at 27.12 and 40.68 MHz, which are the second and third order harmonics of the 13.56 MHz ISM standard frequency.
In the semiconductor industry, throughput is often a very important issue. With large volumes and low profit margins in the more competitive areas, incremental improvements in throughput can provide the necessary edge to compete successfully. In order to reduce manufacturing costs and increase throughput, it is advantageous to process more than one wafer simultaneously. Not only does this reduce the cost of ownership for the process tool, but also, the cost of generating the plasma can be amortized over multiple wafers thereby reducing the production cost per wafer. The difficulty in simultaneously processing multiple wafers in RF reactors is that significant mechanical problems arise. For example, when multiple wafers are processed in the same vacuum chamber and using one RF exciter, the excitation region is about 70 cm in diameter, which would require a very large, thick and heavy dielectric to make the vacuum. For such a three-wafer vacuum chamber, a single quartz piece (dielectric) is projected to be as great as 8 cm thick and weigh greater than 90 kilograms (kg), making it very expensive. Moreover, plasma uniformity is generally an issue if one simply increases the area processed in the RF reactor.
Accordingly, there remains a need for improved apparatuses for processing multiple wafers simultaneously.